The present invention relates to a venting liner, and more particularly to a layered venting liner used in an associated container closure assembly for venting pressure from the container at a specified pressure level.
Venting liners used in container closure assemblies are generally known in the art. When a container is packaged with a product that evolves a gas, or placed in a condition in which excessive pressure might arise, the venting liner allows the excessive pressure to vent from the container into the atmosphere, thus precluding breakage of the closure or the container.
Some venting liners have limited performance and are capable of operating properly only under specific conditions. For example, in some cases, if the closure is threaded to the container with excessive torque, a generally excellent hermetic seal between the liner and the container is obtained, however, because such a strong seal is created under excessive internal pressure, venting may be prevented. This may result in the container bursting, or it would be deformed sufficiently to render it commercially unacceptable to the consuming public. On the other hand, if the closing torque applied to the closure is too low, a hermetic seal might not be obtained, and more importantly the pressurized gas might escape to the atmosphere.
Some venting liners that provide for venting from a container do not maintain a continuous seal with the container, enabling repetitive venting. For example, U.S. Pat. No. 4,121,728 to Tagalakis et al, illustrates a container closure assembly including a venting liner. The venting liner has a breakable seal that disengages the lip of the container to allow excess pressure to vent from the container. The disadvantage of such an arrangement is that once the venting liner breaks from the lip of the container, the liner cannot hermetically reseal with the container lip. The inability to maintain a continuous sealed connection with the container lip, after venting, renders the liner and container susceptible to fluid leakage.
To overcome this problem, venting liners with hydrophobic membranes have been utilized and allow the passage of various gasses from decreasing the pressure of the container while perfecting a seal for containing a liquid. For example, the U.S. Pat. No. 3,951,293 to Schulz, discloses a gas permeable liquid closure for containers of liquids or solids which emit or absorb gas. The closure includes a film of tetrafluoroethylene. The film is supported across an opening of the container by a perforated sealing diaphragm, which is disposed on either one or both sides of the film. Problems have arisen with the use of hydrophobic membrane layers in sealing caps, in that the hydrophobic membranes are most often quite fragile and are unable to perfect a seal between a cap and the lip of an opening of a container resulting in a damaged membrane and imperfect hermetic seal.
Other venting liners permit bi-directional venting, which permits the gas to vent from the container as well as enter the container. U.S. Pat. No. 5,730,306 to Costa et al discloses a venting liner used for bi-directional venting. The liner includes a gas permeable layer that allows gas to exit the container at a specified pressure level, as well as enter the container. Bi-directional venting is unsuitable in cases where the container has been packed with a particular gas to protect the product inside of the container and must maintain only that specific gas in the container in order to preserve the product. The present invention overcomes these problems by providing a venting liner able to vent excess pressure from the container while still maintaining a continuous sealed connection between the liner and container. A further advantage of the present invention is a venting liner, according to the invention, capable of repetitively venting excess pressure while simultaneously preventing liquid from escaping the container by utilizing a pressure responsive expandable layer that enables excessive pressure to vent from the associated container.